Gene Expression-Transcription POGIL Flashcards

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Questions and Answers

Where in the cell is the DNA found?

Nucleus

Where in the cell does transcription take place?

In the nucleus

What polymer is synthesized during transcription?

pre-mRNA

What monomers are used to construct this polymer and where are they found?

Free RNA nucleotides found in the cytoplasm Signup and view all the answers

What enzyme is required for transcription?

RNA polymerase Signup and view all the answers

What is the base-pair rule for a DNA strand matching an RNA strand?

C to G, T to A (DNA), A to U (RNA) Signup and view all the answers

Compare this base-pair rule with that of two DNA strands.

There's no uracil in DNA so T goes with A and A goes with T. In a DNA/RNA match, T goes with A and A goes with U. Signup and view all the answers

Which strand of the DNA contains the 'blueprint' for the pre-mRNA?

The template strand Signup and view all the answers

In which direction is the DNA molecule read?

3' to 5' Signup and view all the answers

In which direction is the pre-mRNA molecule constructed?

5' to 3' Signup and view all the answers

Consider the definition of transcription and explain why the process in Model 1 is described using that word.

To transcribe is to make an exact copy. Transcription is making a copy of the information in DNA as RNA. Signup and view all the answers

What parts make up the transcription initiation complex?

RNA polymerase and transcription factors. Signup and view all the answers

Where on the DNA strand does the initiation complex form?

At the promoter. Signup and view all the answers

Is it likely that a cell would transcribe all the genes within its nucleus simultaneously?

False Signup and view all the answers

Is it likely that all cells transcribe all their genes at some point in their lifetime?

False Signup and view all the answers

What has been removed from the pre-mRNA to make it into mRNA?

Introns Signup and view all the answers

What has been added to the mRNA that was not present in the pre-mRNA, and where on the mRNA strand are the additional items located?

A methyl cap has been added to the 5' end of the mRNA and a poly-A tail has been added to the 3' end of the mRNA. Signup and view all the answers

Identify the structure through which the mRNA leaves the nucleus.

The nuclear pore. Signup and view all the answers

What sequence of bases indicate the starting point for the polypeptide 'blueprint'?

AUG Signup and view all the answers

Why is this molecule called messenger RNA?

The mRNA molecule carries the code for a polypeptide from the nucleus to the cytoplasm. Signup and view all the answers

The human genome contains about 25,000 genes and yet produces about 100,000 different polypeptides. Propose an explanation of how this is possible.

A single sequence of pre-mRNA can produce different mRNA sequences depending on what introns are removed. Signup and view all the answers

Develop a hypothesis to explain the advantage of a poly-A tail added to the 3' end of the mRNA.

It prevents the information-carrying part of the mRNA from being destroyed by the exonucleases before a polypeptide can be formed. Signup and view all the answers

Considering the purpose of adding the poly-A tail, why are some tails longer than others?

An mRNA with a shorter tail will have a shorter lifespan. Proteins that are needed for a long period of time might come from long tail mRNAs whereas proteins that are only needed briefly may come from short-tailed mRNAs. Signup and view all the answers

Summarize the steps of transcription.

Pre-mRNA is made from the template DNA strand, starting at the promoter by the transcription initiation complex. When the RNA polymerase reaches the terminator, the pre-mRNA is released. The methyl cap and poly-A tail get added to make mRNA. Signup and view all the answers

What type of biological molecule is an exonuclease?

Enzyme (protein) Signup and view all the answers

Where do these free nucleotides come from?

They come from the cytoplasm where older mRNA has been hydrolyzed by exonucleases. Signup and view all the answers

How might biologists use transcription mechanisms to support the theory of evolution?

Scientists could use the fact that all species use the same nucleotides in their DNA and mRNA. All species use a promoter region to initiate transcription. All species use a similar RNA polymerase enzyme. Slight variations in the mechanisms could help connect species in an evolutionary phylogenetic tree or cladogram. Signup and view all the answers

Study Notes

Gene Expression-Transcription Overview

DNA is located in the nucleus of a cell.
Transcription occurs within the nucleus, where DNA is copied into RNA.
During transcription, pre-mRNA is synthesized, acting as a precursor to mRNA.
Free RNA nucleotides necessary for constructing pre-mRNA are found in the cytoplasm.

Key Enzyme and Base-Pair Rules

RNA polymerase is the essential enzyme for transcription.
The base-pair rule in DNA and RNA:
- DNA: C pairs with G, T pairs with A
- RNA: A pairs with U (instead of T)

DNA Strands and Transcription Mechanics

The template strand of DNA serves as the "blueprint" for the synthesis of pre-mRNA.
DNA is read from the 3' to 5' direction, while pre-mRNA is constructed in the 5' to 3' direction.
Transcription is accurately described as making an exact copy of DNA's information in RNA form.

Transcription Initiation Complex

The transcription initiation complex consists of RNA polymerase and transcription factors.
This complex forms at a specific region on the DNA called the promoter.

Gene Transcription Regulation

Cells do not transcribe all genes simultaneously; they only transcribe genes as needed to produce specific proteins.
Not all genes are expressed in every cell type; gene expression is selectively turned on or off based on cell location and function.

Post-Transcriptional Modifications

Introns are removed from pre-mRNA to produce the final mRNA.
A methyl cap is added to the 5' end, while a poly-A tail is added to the 3' end of mRNA, contributing to stability and lifespan.

mRNA Processing and Transport

mRNA exits the nucleus through nuclear pores.
AUG is the start codon that signals the beginning of the polypeptide coding sequence.

Function of Messenger RNA

mRNA serves as a messenger carrying the genetic code from the nucleus to the cytoplasm for protein synthesis.

Gene and Protein Diversity

The human genome contains approximately 25,000 genes but can produce around 100,000 different polypeptides through alternative splicing of pre-mRNA.

Poly-A Tail Implications

The poly-A tail extends mRNA half-life, protecting it from exonucleases, allowing for more protein synthesis.
Variations in tail length correlate with mRNA lifespan; longer tails are associated with sustained protein expression.

Summary of Transcription Steps

Initiation: Pre-mRNA synthesis starts at the promoter.
Elongation: RNA polymerase synthesizes pre-mRNA until reaching the terminator.
Termination: Pre-mRNA is released, followed by modifications to form mature mRNA.

Biochemical Role of Exonucleases

Exonucleases are enzymes that degrade RNA, playing a role in mRNA turnover.

Evolutionary Perspectives

Similarities in transcription mechanisms among different species support evolutionary connections, with shared nucleotides and promoter regions indicative of common ancestry.

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Description

Explore key concepts of gene expression and transcription through these engaging flashcards. This quiz will help you understand where DNA is found, the location of transcription, and the molecules involved in the process. Ideal for students looking to reinforce their knowledge in molecular biology.